In multicast and broadcast applications, data are transmitted from a server to multiple receivers over wired and/or wireless networks. A multicast system as used herein is a system in which a server transmits the same data to multiple receivers simultaneously, where the multiple receivers form a subset of all the receivers up to and including all of the receivers. A broadcast system is a system in which a server transmits the same data to all of the receivers simultaneously. That is, a multicast system by definition can include a broadcast system.
The use of unoccupied digital TV spectrum by unlicensed radio transmitters has not before been addressed since the transition of TV broadcasting from analog to digital was only recently completed.
The FCC has issued a ruling that allows the usage of TV white space, i.e., TV channel 2-51 that are not being used by incumbent users, if certain requirements are met. Specifically, WLAN devices need to sense the incumbent usage, need mechanisms for coexistence and resource sharing, and need to adapt their transmission characteristics to fit into one or more digital TV (DTV) channels.